Betaine group-containing derivatives of hydroxyethylcellulose are known from the art. However, these products do not have satisfactory properties when used in cosmetics, especially when used for the preparation of products for the care of hair. It is a further disadvantage of these products that, for their synthesis, reactants are used, which are not absolutely safe physiologically and the complete removal of which from the end product is not readily possible or requires measures, which make the economic use of the compounds impossible.
The Japanese published application 80-43 165 is named as belonging to this state of the art. This application claims amphoteric derivatives of hydroxyethylcellulose, these derivatives being characterized by at least 50 structural units of the general formula ##STR6##
In this general formula
A.sub.1 represents the group --(C.sub.2 H.sub.4 O--).sub.p X.sub.1 PA1 A.sub.2 represents the group --(C.sub.2 H.sub.4 O--).sub.q X.sub.2 PA1 A.sub.3 represents the group --(C.sub.2 H.sub.4 O--).sub.r X.sub.3 PA1 X.sub.1, X.sub.2 and X.sub.3 being either a hydrogen atom or an amphoteric group of the general formula ##STR7## PA1 b is a whole number with a value of 2 to 3, PA1 c is a whole number with a value of 1 to 3, PA1 m is a whole number with a value of 0 to 10, PA1 n is a whole number with a value of 0 to 3, PA1 p is a whole number with a value of 0 to 10, PA1 q is a whole number with a value of 0 to 1, PA1 R' is selected from a group consisting of ##STR11## with the proviso that R'=H when q=0. PA1 R.sup.5 is a divalent aliphatic hydrocarbon group with 1 to 10 carbon atoms,
In this amphoteric group, R.sub.1 and R.sub.2 are a methyl or an ethyl group, m is a whole number from 1 to 6 and n is a whole number from 1 to 2, p, q and r=0 or a whole number not less than 1. The average number of moles of oxyethylene groups per structural unit is 0.5 to 3.0 and the average degree of substitution by amphoteric groups per structural unit is 0.02 to 1.0. It is evident from this description of the formula that the betainic group is linked over ether groups to the cellulose backbone.
Pursuant to the Japanese publication 80-43 165, these compounds are synthesized by, expressed in a simplified fashion, at first reacting an appropriate hydroxyethylcellulose with dialkylaminoalkyl halides of the general formula ##STR8## in the presence of alkali. In the above formula, Y is a halogen atom and the R.sub.1 and R.sub.2 groups and the m subscript have the above meaning. The intermediate obtained is then reacted with a monohalogencarboxylic acid or acrylic acid in the presence of alkali.
For various reasons, this method has proven to be disadvantageous. For instance, the dialkylaminoalkyl halide, used in the first step of the method, is an alkylating agent, which is not entirely safe physiologically and which should not remain in the product, especially if the end products are used in cosmetics. However, it is practically impossible to remove dialkylaminoalkyl halide quantitatively.
A further disadvantage consists therein that the tertiary amine, formed in the first step, reacts more readily with dialkylaminoalkyl halide than do the still unreacted hydroxyethyl groups of the hydroxyethylcellulose. In a side reaction, as a result of the addition reaction with a second dialkylaminoalkyl halide, this then leads to the formation of derivatives with quaternary amino groups, which are present in the end product next to the derivatives with betainic groups. Through the formation of these by-products, however, the compatibility of the products with anionic surfactants is reduced appreciably. This is of disadvantage in the application, since products for the care of hair in many cases contain anionic surfactants as well. The desired advantage in the application of the improved compatibility of compounds containing betaine groups is thus reduced or canceled.
Betaine group-containing derivatives of hydroxyethylcellulose are also disclosed, under certain assumptions, in the U.S. Pat. No. 3,472,840. In this U.S. Patent, a cellulose ether of the general formula ##STR9## which contains a quaternary nitrogen, is claimed. The R.sub.Cell group is an anhydroglucose unit, y is a whole number with a value from 50 to 20,000 and each R represents a group of the general formula ##STR10## in which a is a whole number with a value of 2 to 3,
R.sub.1, R.sub.2 and R.sub.3 in each case represent an alkyl, aryl, aralkyl, alkaryl, cycloalkyl, alkoxyalkyl or alkoxyaryl group with up to 10 carbon atoms. V is a whole number, which corresponds to the valence of X (to shorten it and to make it more understandable, some conditions have been disregarded in this citation).
In this U.S. Patent, the limiting case is mentioned that the anion X can be omitted totally or partly when R' is a carboxyl group, which forms an internal salt with the quaternary ammonium group. In this case, a betaine structure is present. If the anion X is displaced only partly, the disadvantages, inherent in products in which quaternary ammonium groups and betaine groups are present side by side, namely a poor or inadequate compatibility with anionic surfactants, may be observed once again. Cellulose derivatives, the structure of which corresponds to these handicaps, do not form clear aqueous solutions. Moreover, these compounds also do not have satisfactory properties, when they are used in the cosmetic area, especially in cosmetic preparations for the care of hair.